8 ways to preserve food

In this brief guide, we are going to answer the question “8 ways to preserve food” and discuss 8 ways to preserve food along with the benefits and implications of each method.

What are 8 ways to preserve food?

Food preservation involves different food processing steps to maintain food quality at a desired level so that maximum benefits and nutrition values can be achieved. Food spoilage is a natural process; through this process, food gradually loses its color, texture, flavor, nutritional qualities, and edibility. Consumption of spoiled food can lead to illness and in the extreme situation to death. Considering the shelf life, food items can be classified as perishable, semi-perishable, and non-perishable  (1). 

8 common ways to preserve food are:

  1. Freezing
  2. Freeze drying
  3. Dehydrating
  4. Pickling
  5. Fermenting
  6. Canning
  7. Curing with salt
  8. Pasteurisation

Preserving food by freezing

Freezing is the most widely used method of food preservation since it can be done easily at home by anyone and food is preserved for 3 to 12 months. Freezing is especially used for fruits, vegetables and meat products where the original taste and texture needs to be preserved. Individual quick freezing generally relates to quick freezing of solid foods and quick freezing relates to liquid and semi-liquid food. By quick freezing, the ice crystals formed by quick freezing are much smaller and therefore cause less damage to cell structure or texture of the food (1).

Freezing food reduces the enzyme activity in food that causes spoilage. Freezing also crystallizes the water in the food, reducing the amount of liquid water in the food items and diminishes water activity, so microorganisms cannot use it for growth (1).

Freezing itself does not significantly reduce the nutrient content of food. However blanching before freezing and defrosting will cause the loss of some nutrients, mainly water-soluble nutrients such as vitamin C.

Preserving food by freeze drying

Freeze drying is a combination of both freezing and drying. During freeze-drying, the food is frozen and the ice is removed as vapor. Sublimation is the main principle of the freeze-drying process. During sublimation, water is directly converted to vapor without passing through the liquid state in vacuum. For this reason, freeze drying is one of the best methods for preserving bioactive compounds (1).

Freeze-drying preserves food for many years while retaining the nutrient content.

Since freeze drying requires a specifically built freezer dryer, it is usually done only commercially.

Preserving food by dehydrating

Dehydrating is one of the oldest methods of food preservation. Dehydrating works by removing the water from food, thereby reducing the growth of microbes that cause spoilage. Dehydrated food has a long shelf-life and can be stored for up to 5 years under the proper conditions. In this method, the moisture content is lowered to the point where the activities of these microorganisms are inhibited. Bacteria are inactive at water activity below 0.9. Most of the microorganisms cannot grow at water activity below 0.88. Drying reduces weight and volume of foods, facilitates food storage, packaging, and transportation, and also provides different flavors and smells (1).

Food has been dehydrated by natural sun-drying for ages. Now there are electric dehydrators which can be used at homes. Food can also be dehydrated using an oven or a microwave.

Preserving food by pickling

Pickling is a method of preserving food by immersing in a solution of acidic brine or vinegar. 

The production of vinegar is by fermentation of alcohol. Acetobacter converts alcohol to acetic acid in the presence of excess oxygen. Vinegar provides an acidic condition which creates an unfavorable condition for microorganism growth. Under this method, food products are preserved as pickles, relishes, etc (1). 

Pickling adds a distinct flavor to food and pickles are used as side dishes and garnish in many cuisines.

Properly produced pickles can be stored for about a year. However, they must be refrigerated after being opened.

Some commonly pickled fruits and vegetables include mangoes, cucumber, limes and radishes.

Pickles have a high content of sodium due to all the salt added for pickling. So eating large portions of pickles is not recommended. Pickles are also not recommended for people with hypertension and cardiovascular diseases due to the high sodium content. 

Preserving food by fermentation

Fermentation is easily confused with pickling. The difference is that there is no addition of an acidic medium such as acidic brine or vinegar during fermentation. During fermentation, the carbohydrates in food are broken down into acids or alcohols by bacteria and yeast. 

Fermentation preserves most of the nutrients and also produces probiotics. Probiotics are beneficial bacteria that help in maintaining gut health and improving immunity.

There are different types of fermentation used in food processing. Alcohol fermentation is the result of yeast action on the simple sugar (hexose) converting this into alcohol and carbon dioxide. Vinegar fermentation is the conversion of alcohol into acetic acid. Lactic acid fermentation takes place due to the presence of bacteria exclusively to produce flavor in foods, for example in buttermilk, soya sauce and cocoa (1).

Some commonly fermented foods include cheese, yogurt, sauerkraut, wine, beer and sourdough bread.

Preserving food by canning

Canning preserves food by killing the microorganisms that cause spoilage. Canning can be done at home using the correct equipment and proper sterilization of jars but it is time-consuming and needs practice. 

Thermal sterilization is a heat treatment process that completely destroys all the viable microorganisms. Foods with pH above 4.5 require more than 100 °C as sterilization temperature. If the food is not sterilized directly in its final package, but in a heat exchanger equipment, after this, the food is placed in a sterilized package which is then subsequently sealed in an aseptic environment to extend shelf life (1).

Canned foods are shelf-stable for years and do not need refrigeration until they are opened. However, the heating process during canning reduces the nutrient content of food.

Canning is now done on a variety of commercial foods such as beans, corn, tomatoes, pineapple etc.

Preserving food by curing with salt

Curing is an ancient technique that is still being used to preserve food. Curing is done especially to preserve meat and fish. Curing is the process of adding a high content of salt to the meat, followed by drying.

Salt is used as a preservative as it draws out water from the food thereby starving the microorganisms. Salt also kills some microbes by creating a pressure difference and rupturing their cell walls. 

Salt is a natural food preservative. Food preservatives can be classified as natural and artificial. Animals, plants, and microorganisms contain various chemicals which have potential to preserve foods. They also function as antioxidants, flavorings, and antibacterial agents. Other natural food preservatives are sugar and rosemary extract (1).

Cured meat has a very high sodium content. High sodium content has been linked to cardiovascular disease and hypertension

There are health concerns over cured meat. The nitrites and nitrates in curing salts have been associated with certain cancers.

Preserving food by pasteurization

Pasteurization is done by heating food just below the boiling point of water, 100 °C or 212 °F. The heat applied will kill the pathogens and reduce the activity of enzymes that cause spoilage but the bacterial spores survive the pasteurization process.

The efficiency of pasteurization depends on the temperature–time combination. This combination is mostly based on the thermal death-time studies of heat-resisting microorganisms. On the basis of temperature and heat exposure, pasteurization can be categorized as vat (batch), high temperature short time (HTST), and ultra-high temperature (UHT); HTST and UHT are continuous processes (1).

Pasteurization is effectively usually used on dairy products and beverages such as wine, beer and fruits juices. 

The disadvantage of pasteurization is that it will alter the flavor and aroma of food. 

Conclusion

In this brief guide, we answered the question “how to preserve food in 8 ways”. We discussed 8 methods of food preservation and looked at the benefits and implications of each method.

If you have any questions or comments, please let us know.

References

  1. Amit, S.K., Uddin, M.M., Rahman, R. et al. A review on mechanisms and commercial aspects of food preservation and processing. Agric & Food Secur 6, 51 (2017). 
  2. Eun, Jong-Bang, et al. A review of encapsulation of carotenoids using spray drying and freeze drying. Crit Rev Food Sci Nutr, 2020, 60, 3547-3572.